On Linux, extract the bundle(s) and then run: ./start-tor-messenger.desktop

On OS X, copy the Tor Messenger application from the disk image to your local disk before running it.

On all platforms, Tor Messenger sets the profile folder for Firefox/Instantbird to the installation directory.

Note: The policy, unencrypted one-to-one conversations are not allowed and your messages will not be transmitted if the person you are talking with does not have an OTR-enabled client. You can disable this option in the preferences to allow unencrypted communication but doing so is not recommended.